[music playing] This week NASA announced even more evidence of plumes erupting from the surface of Jupiter's moon Europa.
We're becoming increasingly sure that there's a vast ocean of water beneath Europa's icy crust.
But does that ocean have a life?
[music playing] This new evidence of water plumes was found by the Hubble Space Telescope, which took ultraviolet images as Europa passed in front of Jupiter.
Sporadic jets of something appeared to block some of Jupiter's light.
That material seems to be erupting from Europa's South Pole.
This is roughly the same location where a plume of hydrogen and oxygen ions was also seen by Hubble.
The finding makes it even more likely that a vast ocean of liquid water exists beneath Europa's icy crust.
The moon is increasingly looked at as our best chance to find extraterrestrial life in our solar system.
Today I want to talk about why Europa looks so good for life and exactly what form that life might take.
At least on Earth, liquid water is absolutely essential for life.
Every known life form needs at least a little bit.
Having water on Europa doesn't guarantee life there, but it sure makes it more likely.
But Europa isn't the only gas giant moon with a possible ice-covered ocean.
Jupiter's moon Ganymede almost certainly has one, and Callisto may or may not.
Saturn's Enceladus also blasts geysers from its icy surface, so we're pretty sure there's an ocean down there, too.
Europa's probable water vapor plumes make an ocean very likely.
But the moon is extra exciting because of this reddish-brown gunk that covers the surface.
There's a good chance that this is sea salt, perhaps deposited by geysers that produce those plumes and then discolored by Jupiter's intense magnetic field.
A salty ocean tells us that the water must be in direct contact with the rocky surface below.
And for reasons we'll get to, that's pretty important for life to have evolved there.
Ganymede, on the other hand, probably has a vast second layer of ice in between its ocean and the rocky interior.
Saturn's moon Enceladus may be just as promising as Europa.
Its geysers actually produce one of Saturn's rings.
And the Cassini spacecraft found that ring to contain salt.
And why is it so important that the ocean be in contact with the rocky interior?
Well, in general, it's because life needs energy.
We know that the tidal squeezing from Jupiter's gravitational field provides the energy that keeps Europa's ocean liquid.
The same forces drive massive volcanic activity in its system moon IO, and so it's likely that Europa's rocky interior is also geologically active.
There's a good chance that this mains hydrothermal vents.
These may be the perfect place for life-- not just to live, but perhaps to have originally evolved.
In fact, it may be that life on Earth started around its own hydrothermal vents.
This is the iron-sulfur world hypothesis proposed by Gunter Wachtershauser in the 1980s.
The idea is the first simple life came into being around so-called black smokers-- volcanic vents in the deep ocean where noxious gases spew out from Earth's mantle and water temperatures exceed 100 degrees Celsius.
Sounds unpleasant, but the regions around these vents are teeming with life-- 10 to 100,000 times the density of organisms compared to the sea floor.
Entire specialized ecosystems live around Earth's deep sea vents.
The foundation of these are the single-celled organisms that extract energy from the hydrogen sulfide spewing from the vents.
These support all sorts of complex life-- forests of tube worms and clusters of clams and mussels that are crawling with crabs, snails, and shrimp-like amphipods, octopi, and the eel-like [inaudible] top the food chain.
These critters are highly adapted to the extreme temperatures and sulfur-rich environments.
Perhaps the dominant life on Europa are also deep-dwelling, sulfur-munching volcanic sea monsters.
If we believe the iron-sulfur world hypothesis, then deep-sea vents may be where earth life first originated.
It's believed that an energy source and a rich mineral content in liquid water are the main ingredients needed for abiogenesis.
The region surrounding hydrothermal vents have both.
They may have driven a series of peculiar chemical processes, enabled by the energy differential and abundant minerals produced by deep sea black smokers.
These, in turn, may have resulted in a sort of prebiotic chemical metabolism that enabled evolution into true life.
If this is right, there's every reason to hope that the same may have happened on Europa.
But regardless of the truth behind this hypothesis, or even the existence of vents on Europa, if that moon's ocean is in contact with a warm, mineral-rich ocean floor, then perhaps life has found a way.
Now, that Europan ocean is estimated to be 100 kilometers deep, so it's gonna take a long, long while before we can get a probe down to those vents-- if they exist.
However, if life is abundant enough there, then it'll have left its mark on the rest of the ocean-- molecules, isotopic ratios.
Even preferential handedness-- chirality-- of certain molecules can give away the presence of biological processes.
We may find this evidence on or just beneath the icy surface, or even in Europa's vapor plumes.
But if life started at those vents, who's to say it stayed there?
Another promising habitat for Europan life also has an earthly analog-- that's the undersurface of the ice.
That surface is by far the most densely populated region in the oceans beneath the Antarctic Sea ice.
Crevices in caves beneath the ice provide protective habitats.
And the process of melting and refreezing produces an energy gradient that can power metabolisms.
So what does that life look like?
If Earth's ice-loving organisms are anything to judge by, then we're again talking single-celled organisms.
But a number of complex species also live in these frigid environments.
Several types of fish, for example, have antifreeze powers-- proteins that protect their fluids from freezing and livers that can extract ice crystals from their blood.
But why restrict ourselves to the ocean floor or ocean roof?
Life is found throughout earth's oceans.
However, ours are much shallower-- 11 kilometers at the deepest.
And life throughout those depths depends on biological activity at the surface.
Ultimately, their energy and nutrients come from sunlight-powered microorganisms, like algae and plankton, at the ocean's surface.
Europa's ocean roof doesn't have an abundant energy source, and certainly not one that could power a 100-kilometer deep biosphere.
But who knows?
It may be that the ocean floor vents are blasting enough energy and nutrients upwards to support all those alien whale things and tentacled monstrosities and merperson cities that I know we're all really hoping to find.
So when will we know?
NASA's Europa Clipper is expected to launch in the 2020s, and will vastly improve our knowledge of the moon.
The original plan was a lightweight spacecraft carrying several instruments.
It would survey the surface with high-resolution imaging and infrared scans, probe the interior with radar and magnetic mapping, and use a variety of instruments to sniff out the chemical composition of the atmosphere, surface deposits, and the giant vapor plumes.
The observations taken with these instruments would then help NASA decide a promising site for a future possible lander.
However, in its 2016 budget, Congress threw a spinner in the works-- well, sort of.
They allocated a lot more money to NASA's Europa program than requested, but also added a mandate that NASA include a lander on the mission and that it launch by 2022.
That'd be great and all, except it adds a lot of extra weight and development time to the mission, and it also makes it pretty hard for NASA to scout out the best landing spot.
NASA is considering doing this as two separate missions-- if that's even allowed under Congress's decree.
We might wonder whether we should just let NASA do what it does best.
But it's hard to turn down extra funding, so let's see what those geniuses at NASA can come up with.
On the other hand, we may learned a lot-- even before a new probe reaches Europa.
By training Hubble spectrographs on Europa, it may be possible to see the absorption of Jupiter's light, due to specific molecules in those water plumes-- molecules that tell us even more about the plausibility of life in that ocean.
But to really know, we probably do need to land that probe and somehow peer beneath the ice.